The present invention refers to a spiral heat exchanger including at least two spiral sheets extending along a respective spiral-shaped path around a common centre axis and forming at least two spiral-shaped flow channels, which are substantially parallel to each other, wherein each flow channel includes a radially outer orifice, which enables communication between the respective flow channel and a respective outlet/inlet conduit and which is located at a radially outer part of the respective flow channel with respect to the centre axis, and a radially inner orifice, which enables communication between the respective flow channel and a respective inlet/outlet chamber, so that each flow channel permits a heat exchange fluid to flow in a substantially tangential direction with respect to the centre axis, wherein the centre axis extends through the inlet/outlet chambers at the radially inner orifice.
Such a spiral heat exchanger is disclosed in SE 151 318. This known heat exchanger is of a conventional design having a wound centre portion. The heat exchanger is obtained by joining two sheets of metal, introducing the sheets of metal in a split mandrel, and then rolling the sheets to form two concentric spiral channels. Thereafter, the split mandrel is retracted, whereby two semicircular cylindrical spaces are formed, one for each channel, in the centre of the spiral heat exchanger. In order to obtain a sufficient rigidity, stiffeners in the form of rods are frequently positioned in the semicircular spaces to extend in a substantially radial direction.
Another known spiral heat exchanger is provided with a central pipe to which the two spiral sheets are joined. The central pipe is provided with openings giving access to the two flow channels between the spiral sheets. A central sheet is introduced into the pipe in order to provide two semicircular channels providing inlet/outlet chambers for the heat exchange fluids with respect to the two flow channels. In this known design, it is difficult to obtain a proper weld joining the central sheet to the inner surface the central pipe.
SE 80 107 discloses a similar spiral heat exchanger having a central pipe which forms the outlet chamber for one of the spiral flow channels, whereas an annular chamber surrounding the central pipe forms the inlet chamber for the other flow channel.
Spiral heat exchangers are frequently used in applications where the heat exchange fluids contain fibres or other particles. In the prior art heat exchangers the stiffeners and the holes of the central pipe cause clogging of the fibres or particles, which necessitates frequent dismounting and cleaning of the heat exchanger. Also, a central pipe provided with openings is prone to erosion around the openings, especially if the heat exchange fluids contain fibres or particles.
GB 24 404 discloses another type of spiral heat exchanger having a central hollow body. However, there are no inner outlet and inlet chambers positioned in the centre of the heat exchanger. Furthermore, the inner outlet and inlet conduits extend in the same direction through one of the end plates. Due to the eccentric position of the radially inner outlet and inlet conduits, the end plate in question will be subjected to high stresses. Moreover, the design of the inlet and outlet portions of the heat exchanger of this document does not permit a smooth flow of heat exchange fluids.
SE 112 656 discloses a number of different embodiments of spiral heat exchangers, which partly are designed for an axial flow of one of the heat exchange media. A rather complicated construction for a tangential flow application has a centre body provided with inlet and outlet channels arranged within the body, and accessible through longitudinal apertures in the wall of the centre body.
EP 214 589 discloses a spiral heat exchanger having an oblong shape seen in a cross section. The heat exchanger includes a centre body which appears not to be accessible for the heat exchange fluids. However, it appears from this document that the inlet and the outlet channels are displaced with respect to the centre axis of the heat exchanger. Moreover, the design disclosed by EP 214 589 is not suitable for high pressures.
U.S. Pat. No. 4,089,370, U.S. Pat. No. 5,505,255 and U.S. Pat. No. 2,081,678 disclose spiral heat exchangers of another type, which are intended for axial flow through at least one of the flow channels.
The object of the present invention is to provide a spiral heat exchanger, which is designed for tangential flow and which remedies the disadvantages of the prior art heat exchangers referred to above. In particular, it is aimed at a spiral heat exchanger permitting a substantially unobstructed flow of a heat exchange fluid containing fibres or other particles.
This object is obtained by the heat exchanger initially defined, which is characterized in that it includes a centre body extending around the centre axis and being substantially closed with respect to the flow channels and the inlet/outlet chambers.
By providing a closed centre body, the heat exchange fluids will not reach the inner of the centre body, but the fluids may be introduced directly into the flow channels. Consequently the problems of the prior spiral heat exchanger regarding clogging of particles or fibres and erosion of the central structure may be overcome. Furthermore, by such a design the flow area of the flow channel in the inlet and outlet portions will be constant and substantially equal to the flow area in the main part of the flow channels. Thus, it is possible directly upon entry of a heat exchange fluid into the spiral heat exchanger to define an appropriate flow velocity. The flow velocity in the inner inlet and outlet portions of the prior art spiral heat exchanger is often too low, increasing the clogging problems mentioned above. It is essential that the substantially closed centre body means that it does not permit any flow of the heat exchange fluids through the centre body.
According to an embodiment of the invention, the inlet/outlet chamber at the radially inner orifice of one of the flow channels extends from said centre body in one axial direction and the inlet/outlet chamber at the radially inner orifice of the other flow channel extends from said centre body in the opposite axial direction. Consequently, it is possible to obtain two concentric inlet and/or outlet conduits, which is advantageous with respect to the design of the end pieces of the spiral heat exchanger.
According to a further embodiment of the invention, the centre body has a mainly cylindrical shape. In particular, the centre body may have a mainly circular cylindrically shape. Such a circular cross section shape enables a high strength and rigidity of the centre body and the spiral heat exchanger. Advantageously, the centre body has a substantially continuous outer surface. By such a continuous surface, which is uniform without any sharp recesses, sharp ridges or any other edges, an unobstructed flow and a high strength of the centre body may be obtained. Furthermore, the centre body may be substantially concentrical with respect to the centre axis.
According to a further embodiment of the invention the centre body is hollow. Thus, the weight of the spiral heat exchanger may be kept at a low level although the strength of the centre body may be maintained.
According to a further embodiment of the invention, the centre body extends along the centre axis a distance which corresponds to a main part of the width of the spiral sheets in the direction of the centre axis. Thereby, a rigid support for the spiral sheets in the centre of the spiral heat exchanger and an advantageous design of the flow channels in the centre part of the heat exchanger is obtained.
According to a further embodiment of the invention, the spiral heat exchanger includes two end pieces, wherein the spiral sheets and the centre body are arranged between the end pieces. Each end piece may include a centre aperture, through which the centre axis extends wherein each of said orifices is accessible through a respective one of said apertures.
According to a further embodiment of the invention, each of the spiral sheets is joined to the centre body along a line. Said joint lines may be substantially parallel to the centre axis and preferably positioned diagonally opposite to each other with respect to the centre axis.